From what I understand, Nippon orangequat is only as hardy as kumquat, which is only a little bit hardier than Satsuma mandarin.
They're edible, but some people complain that they are not as good eating quality inside as Satsuma (or a regular mandarin), and their outside peel is not as edible as a kumquat. That mixing together the traits of both are not really the most desirable thing for being able to enjoy the fruits.